1. Field of the Invention
This invention relates to a tripod type constant velocity joint incorporated, for example, in the driving system of an automotive vehicle and utilized to transmit a rotative driving force between non-aligned rotary shafts.
2. Related Background Art
In the drive train of a forwardly disposed engine front wheel drive vehicle (FF type vehicle), there arises a case where the portion between the rotary shaft on the wheel side and the rotary shaft on the engine side becomes bent at a relatively great angle. For this reason, to effect transmission of a rotative driving force which is constant, i.e., free of any change in rotational angular speed with rotation, between the two rotary shafts, and enable the automotive vehicle to run smoothly, it is ncessary to connect the two rotary shafts together through a constant velocity joint.
Therefore, it has heretofore been known to use various constant velocity joints to connect the end portions of rotary shafts which are not coaxially aligned with each other. An example will hereinafter be described with reference to FIG. 4 of the accompanying drawings.
In a constant velocity joint 100 according to the prior art shown in FIG. 4, recesses 103 extending in a direction of a first axis are formed in radial directions at equal intervals at three locations (only one of which is shown in FIG. 4) on the inner peripheral surface of a hollow cylindrical housing 102 fixed to the end portion of a first rotary shaft (not shown) such as the rotary shaft on the engine side, and inner side surfaces 104 opposed to each other in the circumferential direction are made into arcuately concave surfaces centered about the axis of the recesses 103.
On the other hand, a tripod 105 fixed to the end portion of a second rotary shaft (not shown) such as the rotary shaft on the wheel side is constructed by securing three pillar-like trunnions 107, radially protruding and extending into the three recesses 103 formed in the housing 102, to the outer peripheral surface of a boss portion 106 to be fixed to the end portion of said second rotary shaft. A spherical roller 108 whose outer peripheral surface is made into a spherical convex surface is rotatably supported around each trunnion 107 through a roller bearing (herein including a needle bearing) 109. The housing 102 and the tripod 105 are combined together by fitting the spherical rollers 108 into the recesses 103 in the inner peripheral surface of the housing 102, thereby constituting the constant velocity joint 100.
In the above-described constant velocity joint 100, when, for example, the first rotary shaft rotates, this rotational force is transmitted from the housing 102 to the boss portion 106 of the tripod through the spherical rollers 108, the roller bearings 109 and the trunnions 107, thereby rotating the second rotary shaft having the boss portion 106 fixed to the end portion thereof. In this fashion, a constant speed is secured between the first and second rotary shafts, as is well known.
It is known that when the prior-art constant velocity joint constructed as described above rotates, rolling frictional resistance and sliding frictional resistance are created on the roller bearings 109 and the spherical rollers 108, respectively, with a result that a force attributable to these resistance forces is created three times per one full rotation in the direction of compression and the direction of tension, axially of the second rotary shaft. By this force created axially of the second rotary shaft, the constant velocity joint 100 is vibrated, and when the rate of these vibrations coincides with the natural frequency of an object such as the vehicle body existing around the constant velocity joint 100, the vibration grows to thereby give discomfort to the seat occupant in some cases.
As a constant velocity joint for preventing the occurrence of vibration which leads to such an inconvenience, there is known one of the structure disclosed in Japanese Utility Model Laid-Open No. 62-49023 or Japanese Patent Application Laid-open No. 63-158327 (corresponding to U.S. Pat. No. 4,854,917). Of these, an embodiment shown in the former will now be described with reference to FIGS. 5 and 6 of the accompanying drawings.
In this constant velocity joint 110, as in the aforedescribed conventional constant velocity joint 100, recesses 113 extending in an axial direction of a first axis are formed at equal intervals in radial directions at three locations in the inner peripheral surface of a hollow cylindrical housing 112 fixed to the end portion of a first rotary shaft 121. However, the inner side surface 126 of each recess 113 is made into a flat surface parallel to a plane including a radial direction of the housing 112 and an axial direction of the recessed portion 113.
On the other hand, a tripod 115 fixed to the end portion of a second rotary shaft 122 such as the rotary shaft on the wheel side is constructed by securing three trunnions 117, for extending into the three recesses 113 formed in the housing 112, to the outer peripheral surface of a boss portion 116 to be fixed to the end portion of the second rotary shaft 122.
Further, in the case of this constant velocity joint 110, an inner guide ring 123 whose outer peripheral surface is made into a spherical convex surface is fitted around each of the three pillarlike trunnions 117. An outer guide ring 124 whose inner peripheral surface is made spherical is fitted around the inner guide ring 123 and further, a cylindrical roller 125 is rotatably supported outwardly thereof through a roller bearing 119.
This improved constant velocity joint 110 is constructed by combining the housing 112 and the tripod 115 together so that the cylindrical rollers 125 supported around the three trunnions 117 are fitted in the recesses 113 in the inner peripheral surface of the housing 112.
The action when the transmission of a rotational force is effected between the first and second rotary shafts 121 and 122 is substantially similar to that in the case of the aforedescribed constant velocity joint 100 (shown in FIG. 4). However, in the case of this constant velocity joint 110, a reduction in the force applied axially of the second rotary shaft 122 can be achieved to thereby prevent the vibration of the constant velocity joint 110.
In the case of the above-described constant velocity joint 110, the following problems newly arise.
As a first problem, mention may be made of the fact that the portions of engagement between the trunnions 117 on the tripod 115 side and the recesses 113 on the housing 112 side become large so that the outer diameter of the constant velocity joint 110 becomes large.
More particularly, the inner guide ring 123, the outer guide ring 124 and the roller bearing 119 are provided between the inner peripheral surface of the cylindrical roller 125 and the outer peripheral surface of each trunnion 117. Since the outer diameter of the trunnions 117 cannot be made small from the viewpoint of maintaining the strength, the outer diameter of each cylindrical roller 125 unavoidably becomes large. An increase in the outer diameter of the cylindrical rollers 125 leads to an increase in the widthwise dimension L of the recesses 113, which in turn leads to an increase in the outer diameter D of the housing 112.
However, it is often the case that the space of the portion of the driving system or the like of an automotive vehicle in which the constant velocity joint 100 or 110 is provided is narrow, and it is preferable that the constant velocity joint not become bulky. Particularly, it becomes difficult to provide the constant velocity joint 110 shown in FIGS. 5 and 6, instead of the costant velocity joint 100 shown in FIG. 4, and to adopt the improved constant velocity joint 110, it will become necessary in some cases to change the design of the surrounding portions such as the shape of the vehicle body.
ln the case of the constant velocity joint described in the aforementioned U.S. Pat. No. 4,854,917, the outer peripheral surfaces of trunnions are made into a spherical shape, whereby the inner guide ring 123 in FIGS. 5 and 6 is eliminated. However, in the necessity of maintaining the strength of the trunnions, it is also difficult to make the outer diameter of the cylindrical rollers small and thus, there has been a similar problem.
As a second problem peculiar to the example of the prior art shown in FIGS. 5 and 6, mention may be made of the fact that it is difficult to make the full length of the rollers constituting the roller bearing 109 great, and thus the rotational resistance of the roller bearing 109 is liable to become great. That is, to make the outer diameter of the constant velocity joint 110 (the outer diameter D of the housing 112) small on the assumption that the outer diameters of the cylindrical rollers 125 are the same, it is effective to dispose all of the cylindrical rollers 125 and the members 123, 124 and 119 existing between them and each trunnion 117 inside the smallest circumscribed circle of the three trunnions 117 secured to the tripod 115. However, if this condition is satisfied and yet the roller bearing 119 is provided between the outer peripheral surface of the outer guide ring 124 and the inner peripheral surface of the cylindrical roller 125 as shown in FIG. 5. The rollers constituting the roller bearing 119 will be become small in length.
If the length of the rollers constituting the roller bearing 119 becomes small, each roller becomes liable to be inclined (skew) with respect to the center axis of the roller bearing 119 (which coincides with the center of the trunnion). If the rollers skew, the rolling resistance of the roller bearing 119 will become great and the resistance to relative displacement between the cylindrical rollers 125 and the inner side surfaces of the recesses 113 of the housing 112 will become great.
If the rollers are retained by a retainer to prevent skew, not only the cost of manufacture will increase due to an increase in the number of parts, but also the number of rollers assembled between the outer guide ring 124 and the cylindrical rollers 125 must be reduced. Thus, the load applied to each roller will increase and, fretting wear becomes liable to occur. For this reason, it is preferable not to use a retainer.
In another embodiment shown in the aforementioned Japanese Utility Model Laid-Open No. 62-49023, there is described a construction in which a cylindrical roller whose outer peripheral surface is made into a cylindrical surface is fitted to a spherical roller rotatably supported on the outer peripheral surface of a trunnion through a roller bearing. Because the widthwise dimension of the cylindrical roller is greater than the widthwise dimension of the spherical roller, the configuration of a housing having recesses into which the trunnions extend cannot be made small and thus, the constant velocity joint cannot be made compact. If an attempt is made to make the constant velocity joint compact, the full length of a plurality of rollers constituting a roller bearing will become small and the rolling resistance of the roller bearing will be liable to become great.